Aggregation of tropical urban soils in the metropolis of São Paulo, southern Brazil

Abstract

This study investigated the interplay between the mechanisms of natural soil formation and human-induced alterations in tropical urban soils in São Paulo, Brazil, in order to understand soil dynamics, which are crucial for sustainable urban soil management. Through comprehensive field surveys and laboratory analyses, three soil pedons from Villa Lobos Park (São Paulo city), which was inaugurated in 1994, were studied. To carry out the research, morphological, chemical, physical and micromorphological analyses, as well as aggregate scanning, were conducted. A correlation matrix was created for each pedon to statically analyze the data. The results revealed that the soil composition and aggregation dynamics in Villa Lobos Park were influenced by both natural pedogenic processes and anthropogenic interventions. Over three decades, organic carbon enrichment from root decay and grass biomass decomposition has improved soil quality through melanization. Additionally, inherited organic matter (OM) amounts from technogenic deposits and deliberate OM additions during the establishment of the park have enhanced the organic content near the soil surface. Also, calcification is present. Aggregation dynamics are governed by factors such as aromatic humus, polysaccharide polymers, the synergistic action of fauna and roots, and facilitated by the wetting–drying cycles of the tropical climate and the abundance of cations, notably Ca²⁺. Rapid macroaggregate formation driven by the wetting–drying cycles and the extensive root networks was observed, combined with slower microaggregate development facilitated by the interaction of polysaccharides and organic-minerals complexes. Anthropogenic inputs, including clayey layers, construction residues, organic matter supplements, earthworm populations, and grass cultivation, significantly shaped soil aggregation dynamics, accelerating pedogenic transformations and improving the overall quality of the soil within the park. Understanding these dynamics is crucial for sustainable soil management in urban green spaces like the Villa Lobos Park, offering insights into effective conservation and restoration strategies in similar urban environments worldwide.